A schematic diagram of the ¯ow system is shown in Fig. 1. In this system, a sample solution pumped at 1.57 ml/min merged with 1 mol/l thiocyanate solution stream at a ¯ow rate of 1.59 ml/min and it percolates the polyurethane foam minicolumn. The interferent ions were held on the PUF minicolumn as thiocyanate complexes. Under these conditions, the remaining solution containing Ni(II) (not held in the PUF mini-column because Ni-thiocyanate complex is not formed) ®lled the sample loop (L). This step (separa-tion and loading) took place in 30 s. By switching the commutator, the measurement and cleaning step starts. Sample into the loop (L) was displaced by a water carrier stream pumped at 1.54 ml/min, merged with reagent (PAR) at a rate of 0.57 ml/min and after mixing in a 380 ml reactor coil (R) the absorbancewas measured at 498 nm (D). Simultaneously, a cleaning